COMPARATIVE STUDY OF CHANGES IN PHARYNGEAL...

COMPARATIVE STUDY OF CHANGES IN PHARYNGEAL AIRWAY

DIMENSION AND HYOID BONE POSITION FOLLOWING

NONSURGICAL ORTHODONTIC TREATMENT IN

CLASS I AND CLASS II SUBJECTS

Dissertation Submitted to

THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY

In Partial fulfilment for the degree of

MASTER OF DENTAL SURGERY

BRANCH - V

ORTHODONTICS AND DENTOFACIAL ORTHOPAEDICS

APRIL – 2013

CERTIFICATE

This is to certify that the dissertation entitled

“COMPARATIVE STUDY OF CHANGES IN PHARYNGEAL AIRWAY

DIMENSION AND HYOID BONE POSITION FOLLOWING NONSURGICAL

ORTHODONTIC TREATMENT IN CLASS I AND CLASS II SUBJECTS” done

by Dr. N.M.VIJAYKUMAR Post graduate student (M.D.S), Orthodontics

(branch V), Tamil Nadu Govt. Dental College and Hospital, Chennai, submitted to

the Tamil Nadu Dr. M.G.R. Medical University in partial fulfilment for the M.D.S.

degree examination (April 2013) is a bonafide research work carried out by him

under my supervision and guidance.

Guided By

Dr. M.C.SAINATH M.D.S.,

Professor and Head of the Department,

Dept. of Orthodontics,

Tamil Nadu Govt Dental College & Hospital,

Chennai - 600 003

Dr. K.S.G.A. NASSER, M.D.S.,

Principal,

Tamil Nadu Govt Dental College, & Hospital,

Chennai - 600 003.

DECLARATION

I, Dr. N.M.VIJAYKUMAR , do hereby declare that the dissertation titled

“COMPARATIVE STUDY OF CHANGES IN PHARYNGEAL AIRWAY

DIMENSION AND HYOID BONE POSITION FOLLOWING NONSURGICAL

ORTHODONTIC TREATMENT IN CLASS I AND CLASS II SUBJECTS” was

done in the Department of Orthodontics, Tamil Nadu Government Dental College

& Hospital, Chennai 600 003. I have utilized the facilities provided in the

Government Dental College for the study in partial fulfilment of the requirements

for the degree of Master of Dental Surgery in the speciality of Orthodontics and

Dentofacial Orthopaedics (Branch V) during the course period 2010-2013 under the

conceptualization and guidance of my dissertation guide, Professor Dr. M. C.

Sainath, MDS.

I declare that no part of the dissertation will be utilized for gaining financial

assistance for research or other promotions without obtaining prior permission from

the Tamil Nadu Government Dental College & Hospital.

I also declare that no part of this work will be published either in the print or

electronic media except with those who have been actively involved in this

dissertation work and I firmly affirm that the right to preserve or publish this work

rests solely with the prior permission of the Principal, Tamil Nadu Government

Dental College & Hospital, Chennai 600 003, but with the vested right that I shall

be cited as the author(s).

Signature of the PG student Signature of the HOD

Signature of the Head of the Institution

ACKNOWLEDGMENT

My sincere thanks to Dr. K.S.G.A. NASSER, M.D.S., Principal, Tamil

Nadu Government Dental College and Hospital, Chennai-3, for his kind support

and encouragement.

I express my deep sense of gratitude and great honour to my respected

guide, Professor Dr. M.C.SAINATH M.D.S., Head of the Department,

Department of Orthodontics and Dentofacial orthopaedics, Tamilnadu Govt. Dental

College and Hospital, Chennai-3, for his patience guidance, support and

encouragement throughout the study.

I owe my thanks and great honour to Dr. G. VIMALA M.D.S, Professor,

Department of Orthodontics and Dentofacial Orthopaedics, Tamilnadu Govt.

Dental College and Hospital, Chennai3, for helping me with her valuable and

timely suggestions and encouragement.

I owe my thanks and great honour to Dr.S.PREMKUMAR M.D.S,

Professor, Department of Orthodontics and Dentofacial Orthopaedics, Tamilnadu

Govt. Dental College and Hospital, Chennai3, for helping me with his valuable and

timely suggestions and encouragement.

I am grateful to Dr.B.BALASHANMUGAM, M.D.S., Assistant

Professor, Department of Orthodontics, Tamil Nadu Government Dental College

and Hospital, Chennai –3 for his support and encouragement.

I am grateful to Dr. USHA RAO, M.D.S., Assistant Professor, Department

of Orthodontics, Tamilnadu Government Dental College and Hospital, Chennai-3

for her support and encouragement.

I am grateful to Dr. K. USHA, M.D.S., Assistant Professor, Department of

Orthodontics, Tamil Nadu Government Dental College and Hospital, Chennai –3

for her support and encouragement.

I thank Dr. R. RAVANAN M.Sc., M.Phil., Ph.D., Professor of Statistics,

Presidency College, for helping me with the Statistics in the study.

I take this opportunity to express my gratitude to my friends and colleagues

for their valuable help and suggestions throughout this study.

I offer my heartiest gratitude to my family members for their selfless

blessings.

I seek the blessings of the Almighty God without whose benevolence; the

study would not have been possible.

TRIPARTITE AGREEMENT

This agreement herein after the “Agreement” is entered into on this

day............... day of December 2012 between the Tamil Nadu Government Dental College

and Hospital represented by its Principal having address at Tamilnadu Government

Dental college and Hospital, Chennai-03, (hereafter referred to as , ’the college’)

And

Dr. M. C. Sainath aged 55 years working as professor at the college, having residence

address at Block ‘U’, Door no 11,4th main road, Annanagar, Chennai 600040, Tamilnadu

(herein after referred to as the ‘Principal investigator’)

And

Dr. N.M.VIJAYKUMAR aged 28 years currently studying as postgraduate student in

department of Orthodontics in Tamilnadu Government Dental College and Hospital

(herein after referred to as the ‘PG/Research student and co- investigator’).

Whereas the ‘PG/Research student as part of his curriculum undertakes to

research on “Comparative study of changes in pharyngeal airway dimension and hyoid

bone position following nonsurgical orthodontic treatment in class I and class II

subjects.” for which purpose the PG/Principal investigator shall act as principal

investigator and the college shall provide the requisite infrastructure based on availability

and also provide facility to the PG/Research student as to the extent possible as a Co-

investigator.

Whereas the parties, by this agreement have mutually agreed to the various issues

including in particular the copyright and confidentiality issues that arise in this regard.

Now this agreement witnesseth as follows:

1. The parties agree that all the Research material and ownership therein shall become the

vested right of the college, including in particular all the copyright in the literature

including the study, research and all other related papers.

2. To the extent that the college has legal right to do go, shall grant to licence or assign the

copyright do vested with it for medical and/or commercial usage of interested

persons/entities subject to a reasonable terms/conditions including royalty as deemed by

the college.

3. The royalty so received by the college shall be equally by all the parties.

4. The PG/Research student and PG/Principal Investigator shall under no circumstances

deal with the copyright, Confidential information and know – how generated during the

course of research/study in any manner whatsoever, while shall sole vest with the manner

whatsoever and for any purpose without the express written consent of the college.

5. All expenses pertaining to the research shall be decided upon by the principal

investigator/Co-investigator or borne sole by the PG/research student.(co-investigator)

6. The college shall provide all infrastructure and access facilities within and in other

institutes to the extent possible. This includes patient interactions, introductory letters,

recommendation letters and such other acts required in this regard.

7. The principal investigator shall suitably guide the student Research right from selection

of the Research Topic and Area till its completion. However the selection and conduct of

research, topic and area research by the student researcher under guidance from the

principal investigator shall be subject to the prior approval, recommendations and

comments of the Ethical Committee of the college constituted for this purpose.

8. It is agreed that as regards other aspects not covered under this agreement, but which

pertain to the research undertaken by the student Researcher, under guidance from the

Principal Investigator, the decision of the college shall be binding and final.

9. If any dispute arises as to the matters related or connected to this agreement herein, it

shall be referred to arbitration in accordance with the provisions of the Arbitration and

Conciliation Act, 1996.

In witness whereof the parties hereinabove mentioned have on this the day month and year

herein above mentioned set their hands to this agreement in the presence of the following

two witnesses.

College represented by its Principal PG Student

Witnessess Student Guide

1.

2.

CONTENTS

Sl.No. Title Page No.

1. INTRODUCTION 01

2. AIM AND OBJECTIVES 05

3. REVIEW OF LITERATURE 06

4. MATERIALS AND METHODS 28

5. STATISTICAL ANALYSIS 39

6. RESULTS 40

7. DISCUSSION 55

8. SUMMARY AND CONCLUSION 64

9. BIBLIOGRAPHY 66

List of tables

S.no Table Page no.

1. Cephalometric Landmarks 30

2. Airway Parameters 32

3. Hyoid Bone Position Parameters 32

4. Dentofacial parameters 32

5. Distribution of study subjects - based on gender 40

6. Distribution of study subjects based on age. 41

7. Comparison of Airway related parameters among study subjects

within Class I malocclusion group

42

8. Comparison of Hyoid position related parameters among study

subjects within Class I malocclusion group

42

9. Comparison of Dento-facial related parameters among study

subjects within Class I malocclusion group.

43

10. Comparison of Airway related parameters among study subjects

within Class II malocclusion group.

44

11. Comparison of Hyoid position related parameters among study

subjects within Class II malocclusion group.

44

12. Comparison of Dento-facial related parameters among study

subjects within Class II malocclusion group.

45

13. Comparison of airway parameters between Class I and Class II

malocclusion groups.

46

14. Comparison of Airway Parameters between Class I And Class II

Malocclusion Groups Independent Samples Test

47

15. Comparison of hyoid position related parameters between Class

I and Class II malocclusion groups.

49

16. Comparison of hyoid position related parameters between

subjects with Class I and Class II occlusion - Independent

Samples Test

49

17. Comparison of airway related parameters between subjects with

Normal, Class I and Class II occlusion at baseline

51

18. Comparison of airway related parameters between subjects with

Normal, Class I and Class II occlusion -post treatment.

51


subjects with Normal, Class I and Class II occlusion at baseline.

52


subjects with Normal, Class I and Class II occlusion-post

treatment.

52

21. Changes In Airway dimension And Hyoid bone position -

Based On Gender

53

List of colour plates

1. Cephalostat

2. Canon D520 MF scanner

3. Standardization with Transparent Grid

4. Standardization with Adobe photoshop CS5

5. Ax Ceph Cephalometric Analysis Software

6. Analysis of digitized lateral cephalograms – Control subject

7. Analysis of digitized lateral cephalograms – Class I subject

Pretreatment and post treatment.

8. Analysis of digitized lateral cephalograms – Class II subject

Pretreatment and post treatment.

Abstract

Background: Pharyngeal airway dimensions, narrowing of pharyngeal passage and hyoid bone

positions are of interest in orthodontics .It is evident that there exists a mutual correlation

between position of the hyoid bone, volume of pharyngeal airway and dentofacial structures.

Therefore it is relevant to evaluate the changes in nasopharyngeal airway and hyoid bone

position in subjects with moderate dentofacial deformities, who had orthodontic treatment. This

retrospective, analytical cephalometric study had been undertaken to investigate correlation in

skeletal Class I and skeletal Class II subjects who had undergone non-surgical orthodontic

treatment.

Aim: The aim of this study was to evaluate and compare the changes in pharyngeal airway

dimension and hyoid bone position following non-surgical orthodontic treatment in Class I and

Class II dentofacial deformities.

Materials and methods: 40 sets (pre & post treatment ) of lateral cephalograms of subjects (20

skeletal Class I & 20 skeletal Class II malocclusion) were analysed. The control group consisting

of 20 lateral cephalograms of subjects with normal occlusion and good visibility of hyoid bone

were used .All cephalograms were taken in natural head position, with PLANMECA PM 2002

CC PROLINE machine. All the radiographs were scanned with CANON D520 MF scanner and

digitized. A Cephalometric analysis software AX CEPH version 2.3.0.74 was used to analyse the

radiographs.

Results: Pretreatment hypopharynx area was significantly constricted in both Class I and Class

II groups with highly significant reduction (p value < 0.001) in Class II groups in comparison

with normoocclusion group. In Class I malocclusion group there was a significant decrease in

overall upper airway dimensions, with more reduction in glossopharynx and hypopharynx areas

following orthodontic treatment with only velopharynx and glossopharynx areas approximating

to the values of the normoocclusion group. In Class II malocclusion the glossopharynx and

hypopharynx areas were widened significantly, still the hypopharynx area was not widened to

the level of normoocclusion group. After treatment the hyoid was retracted postero inferiorly in

Class I group and in Class II group the hyoid bone was shifted anterosuperiorly. Still the hyoid

position was not approximated to that of normoocclusion group. There was no statistically

significant (p value > 0.05) sexual dimorphism in both pharyngeal airway dimensions and hyoid

bone positions in all three groups.

Conclusion: There is a definite difference in pharyngeal airway dimension and hyoid bone

position in different malocclusions. It was evident that Non-surgical orthodontic treatment had a

significant influence on the pharyngeal airway dimensions and hyoid bone positions in Class I

and Class II malocclusion corrections.

Key Words: Pharyngeal Airway, Hyoid Bone, Lateral Cephalograms, Class I & Class II

Malocclusion.

Introduction

1

Introduction

Pharyngeal airway dimensions and resistance are of interest in

orthodontics. Ever since, several studies have indicated a close association

between airway dimensions and dentofacial structures20, 24

. Numerous

evidences from cephalometric studies support a link between airway

dimensions, hyoid bone positions and maintenance of dentofacial harmony.

The pharynx is a 12–14 cm long musculomembranous tube shaped like

an inverted cone 29

. It extends from the cranial base to the lower border of the

cricoid cartilage (the level of the sixth cervical vertebra), where it becomes

continuous with the oesophagus73

.

The pharynx communicates with the nasal, oral and laryngeal cavities

via the nasopharynx, oropharynx and laryngopharynx respectively45

. The

nasopharynx and the oropharynx have significant locations and functions as

they form a part of the unit in which respiration and deglutition are carried out.

The nasopharynx forming the upper part of respiratory system is connected

anteriorly with nasal cavity and posteriorly it extends as oropharynx. The

oropharynx extends from the soft palate to the base of epiglottis (from second

to fourth cervical vertebra). The laryngopharynx joins the oropharynx at the

level of pharyngoepiglottic fold and the hyoid, and then it continues upto the

level of the sixth cervical vertebra.

The pharynx is composed of three coats: mucous,

fibrous, and muscular. The muscles of the pharynx are three circular

Introduction

2

constrictors and three longitudinal elevators. The constrictors may be thought

of as three overlapping cones which arise from structures at the sides of the

head and neck and pass posteriorly to insert into a midline fibrous band, the

pharyngeal raphe (overlapping has been compared with that of three flower

pots placed one inside another)73

. Its lining mucosa is continuous with that

lining the pharyngotympanic tubes, nasal cavity, mouth and larynx 29

.

Nasal obstruction due to anatomical variations and pathologies can

cause chronic mouth breathing and a number of postural changes, such as open

mandibular posture, downward and forward positioning of the tongue, and

extension of the head. If these postural changes continue during the active

growth stage without any restrictions, over a period of time many dentofacial

disorders at different levels of severity can be seen, such as long face syndrome

or adenoid facies51

. Other than these factors there is also the natural anatomical

predisposition of narrower airway passages. Skeletal features such as retrusion

of the maxilla and mandible and vertical maxillary excess in hyperdivergent

patients may lead to narrower anteroposterior dimensions of the airway75

.

Obstructive sleep apnoea is a serious medical problem and may be

precipitated by any narrowing of the upper airway caused by external or

internal factors. Investigators have reported a steeper mandibular plane angle,

shorter mandibular body length and a low hyoid bone position in patients

suffering from obstructive sleep apnoea.

Hence pharyngeal study is of importance to both otolaryngologists and

orthodontists alike.

Introduction

3

According to the Balter's philosophy, Class II malocclusions are a

consequence of a backward position of the tongue, due to which the normal

respiratory function is impeded and thus resulting in a faulty deglutition and

mouth breathing; while Class III malocclusions are due to a more forward

position of tongue28

.

The size of nasopharyngeal area is significantly greater in Class I than in

Class II malocclusions20

. Hence a significant interaction is expected to occur

between the pharyngeal structures and dentofacial pattern.

The hyoid bone is a horseshoe-shaped bone situated in the anterior

midline of the neck between the chin and the thyroid cartilage. At rest, it lies at

the level of the base of the mandible in the front and the third cervical

vertebra behind29, 45

. Unlike other bones of neck hyoid does not have any bony

articulations. It provides attachments for ligaments, muscles, fascia of cranium

and mandible. The two major group of muscles attached to hyoid bone are

suprahyoid and infrahyoid muscles. Both suprahyoid and infrahyoid muscles

have wide range of actions.

Digastric muscle is one of the suprahyoid muscles increase the antero

posterior dimensions of oropharynx during deglutition. The stylohyoid and

posterior belly of digastric act together to prevent the regurgitation of food49

.

The hyoid bone plays an important and active part in accomplishing the

delicate balance between anterior and posterior muscle tension relative to the

http://en.wikipedia.org/wiki/Bone

http://en.wikipedia.org/wiki/Neck

http://en.wikipedia.org/wiki/Chin

http://en.wikipedia.org/wiki/Thyroid_cartilage

http://en.wikipedia.org/wiki/Human_mandible

http://en.wikipedia.org/wiki/Cervical_vertebra

http://en.wikipedia.org/wiki/Cervical_vertebra

Introduction

4

occipital condyles, which in turn helps to balance the head as man assumed an

upright posture.

It is evident that there exists a mutual correlation between position of the

hyoid bone, volume of pharyngeal airway and dentofacial structures. In all

types of dentofacial deformities there is a difference in position of dentofacial

structures including teeth. Therefore it is relevant to evaluate the changes in

nasopharyngeal airway and hyoid bone position in subjects with moderate

dentofacial deformities, who had orthodontic treatment. The methods for

evaluating pharyngeal dimension in orthodontic practices are limited.

This retrospective, analytical cephalometric study had been undertaken

to investigate such correlation in skeletal Class I and skeletal Class II subjects

who had undergone non-surgical orthodontic treatment with extraction of four

premolar teeth and comparing it with normoocclusion subjects.

Aim and Objectives

5

AIM AND OBJECTIVES

AIM:

The aim of this study was to evaluate and compare the changes in

pharyngeal airway dimension and hyoid bone position following non-

surgical orthodontic treatment in Class I and Class II dentofacial deformities.

OBJECTIVES:

To determine whether the pharyngeal airway dimensions and hyoid

bone position were affected by non-surgical orthodontic treatment in

skeletal Class I & skeletal Class II subjects.

To evaluate the pharyngeal airway dimensions and hyoid bone position

in normal subjects of South Indian origin.

To compare the changes of pharyngeal airway dimensions and hyoid

bone positions between these groups.

To determine any sexual dimorphism in the changes of pharyngeal

airway dimensions and hyoid bone positions following non-surgical

orthodontic treatment in both Class I and Class II groups.

Review Of Literature

6

Review of literature

The Pharyngeal airway is composed of 20 or more muscles that are

attached proximally to skeletal structures and those size and form are affected

by the developing craniofacial skeleton. The oral and pharyngeal regions are

said to have a primary function in maintaining a patent airway. This is

accomplished by a dynamic musculoskeletal balance. The pharyngeal airway is

one of the determinants of anteroposterior relationship of jaws, particularly the

mandible; by means of determining the tongue position. Accordingly, the

dimensions of pharynx are determined by the position and relation of the

maxilla and the mandible. Moss56

while explaining the functional matrices goes

one step further by including the pharynx into the oro-naso-pharyngeal

functioning spaces, whose volumetric growth is primary morphogenetic event

in facial skull growth. The literature related to the development of pharyngeal

airway and hyoid bone position and their association with the various

malocclusions has been reviewed here.

Balters28

(1952) had a unique view as far as the aetiology of the development

of malocclusion was concerned. According to his hypothesis, Class II

malocclusions were a consequence of a backward position of the tongue which

impedes the respiratory function, concomitantly leading to narrower

pharyngeal airway and mouth breathing. By the same analysis, he reasoned that

Class III conditions are due to a more forward position of tongue and

consequently larger pharyngeal airway dimensions.


7

Allan G. Brodie2 (1952) discussed the role of musculature in diagnosis,

treatment and retention. According to him, the hyoid and the tongue are

intimately associated structures and both are positioned in space by a 3 point

muscular suspension.

Carmine Durzo et al14

(1962) studied the growth behaviour of the hyoid bone

in relation to other craniofacial structures in a longitudinal cephalometric study.

They concluded that the hyoid bone has a stable vertical position in normal

individuals, at a level opposite the lower portion of third and upper portion of

fourth cervical vertebra. During growth its relative position remains constant

when it descends as the cervical vertebrae increase their length and the cranial

base and mandible descend and move away from each other. In the mandibular

deformity cases the hyoid movements followed closely those of mandibular

growth movements and were restricted both anteroposteriorly and vertically.

The hyoid movements were also modified as per the demands of maintaining a

patent airway.

Reul Bench74

(1963) carried out an elaborate cephalometric study on the

growth of the cervical vertebra as related to tongue; face and denture

behaviour. He concluded that, in older ages, the behaviour of the hyoid bone is

more consistent to the growth of the cervical vertebrae than chin growth. At 3

years of age the hyoid lies at a level between 3rd and 4th cervical vertebrae and


8

descends to the level of the 4th vertebrae at adulthood. Furthermore the clinical

manifestations of open bite are characterized by unusual position and behaviour

of the hyoid bone. He noted that in dolichocephalic persons there was a more

vertical descent of the hyoid bone than in brachycephalic persons. However the

latter was characterized by a more anterior growth shift of the hyoid bone. It

was postulated that the descent and retraction of the tongue seemed to offer one

explanation of the late crowding that develops in the anterior region of the

lower dental arch following orthodontic treatment or in normal untreated cases.

Robert Sloan et al71

(1967) using cineflurography compared the hyoid

movement during deglutition in Class I and Class II patients. They concluded

that in Class I malocclusion patients, the hyoid bone was found to be positioned

more posteroinferiorly and showed the greatest range of vertical movement

during deglutition. It also showed the most limited functional pattern in this

group. In Class II patients, the hyoid was positioned more upwards and

forwards or anterosuperiorly to the mandible and showed the greatest range

during deglutition. The authors confirmed two patterns of hyoid bone

movement during deglutition-Circular and Oblique or Elliptical.

Moss56

(1969) in his functional matrix theory of facial growth, states that the

changes in cell size, shape and spatial position, and indeed the very

maintenance of all the skeletal units; are always secondary to the primary


9

changes in their functional matrices. He called pharynx as, a part of one of the

primary functional spaces – the oro-naso-pharyngeal functioning space

(orofacial capsular matrix); and it is the volumetric expansion of these

pharyngeal, oral and nasal spaces that causes the translation of all the skeletal

units embedded within the orofacial capsule.

Ian Milne and John Cleal37

(1970) evaluated the functional adaptation of

orofacial structures in a cineflurographic study. They concluded that the hyoid,

the tongue and the mandible worked as an integrated unit. The positional

changes of the hyoid bone are characteristics of the integration of numerous

structures involved in deglutition. The tongue tip and pharyngeal structures are

capable of acting in part, autonomously and the adaptive movements of the

hyoid are responsible for the maintenance of an adequate airway.

Gary Cuozzo and Douglas Bowman27

(1975) shed light on the changes in the

hyoid bone during deglutition following forced distal positioning of the tongue

by a tongue crib. The conclusions suggested that in persons with the hyoid

resting close to the mandible, the hyoid bone moved in a posteroinferior

direction following crib placement and in persons where hyoid rest position

was distant from the mandible, the hyoid bone did not show any positional

change following crib placement. They attributed these differences to the


10

limitation of posterior displacement of the hyoid bone in need for maintaining a

patent airway.

Garland Hershey.H et al26

(1976) in their study of Changes in nasal airway

resistance associated with rapid maxillary expansion with six boys and eleven

girls (between 11 and 14 years of age) who had mouth breathing, concluded

that rapid maxillary expansion was not only an efficient method for increasing

the width of narrow maxillary arches but also reduces nasal resistance from

levels associated with mouth breathing to levels compatible with normal nasal

respiration.

David Gobielle and Douglas Bowman21

(1976) illustrated the hyoid bone and

muscle changes in 10 children, 11 to 15 years of age, after distal positioning of

the tongue. They concluded the following,

a. The hyoid bone assumed a posteroinferior position in individuals with the

rest position of the hyoid bone near the mandible and in individuals with hyoid

rest position distant from the mandible, there was no change in hyoid position

after distal tongue repositioning.

b. There was no change in hyoid path during deglutition before and after distal

tongue positioning.


11

Proffit68

(1978) explained that if there was difficulty in breathing due to airway

obstruction, the physiologic adaptation that facilitate mouth breathing include a

forward posture of head and a lowered position of the mandible with a low and

forward tongue posture.

Lee Graber48

(1978) correlated pre and post treatment hyoid positions after

chin cup therapy in 30 individuals of average 6 years of age using lateral

cephalograms. He found that the hyoid bone followed the posteroinferior

direction of mandibular rotation during the course of treatment. He concluded

his result to be attributed to the tongue repositioning and the proximity of the

oropharyngeal and laryngeal spaces to the hyoid bone.

Bibby and Preston10

(1981), described the hyoid triangle analysis. After an

extensive study of the literature, he concluded that the vast variation found in

the previous studies may be because of the fact that the hyoid bone was

correlated to cranial structures. The hyoid, by virtue of being totally suspended

by soft tissues and located away from the cranial structures, any small variation

in the position of the reference planes due to head position changes would

result in a much greater apparent variation of the hyoid bone.

In their analysis, they related the hyoid bone to the vertebrae and the mandible.

Since the mandibular symphysis is at a level more comparable to the axis of

rotation of the head than the cranium, the effect of head movement was


12

minimized and the hyoid position was determined more accurately. He had

given standard values for the hyoid triangle and also concluded that there is no

sexual dimorphism in the position of the hyoid.

Ioannis P.Adamidis et al38

(1983) evaluated the position of the tongue,

mandible and hyoid bone in children aged 9 years having lymphadenoid

hypertrophy, mouth breathing and Class I malocclusion. They concluded that

the tongue was placed more downwards and forwards in the lymphadenoid

hypertrophy group. The mandible showed a clockwise rotation and a

significant downward inclination, increased lower anterior facial height and

increased gonial angle in lymphadenoid hypertrophy group. The hyoid bone

was found to follow the mandibular inclination and was found to rotate and

attain a more inferior direction in the lymphadenoid hypertrophy group.

Bibby11

(1984) used his hyoid triangle analysis to evaluate the hyoid bone

position in mouth breathers and tongue thrusters and compared to a control

sample. The results did not show any significant differences in hyoid bone

position in the three groups compared and he concluded that the hyoid has a

stable position independent or any posture alterations due to tongue thrusting or

mouth breathing.


13

McNamara41

(1984) suggested that lower pharyngeal width can be measured

from the intersection of posterior border of tongue and inferior border of the

mandible to the closest point on the posterior pharyngeal wall. He felt that the

width of the lower pharynx greater than 15 mm suggested anterior positioning

of the tongue.

Athanasiou et al8 (1991) studied the changes in pharyngeal depth and hyoid

bone at the level of 2nd

and 4th

cervical vertebrae and their relationship in

mandibular prognathism in lateral cephalograms of patients who received

combined orthodontic-surgical treatment. The hypothesis that posterior

mandibular repositioning may reduce the airway at the levels of 2nd

and

4thcervical vertebrae cannot be supported by the findings of this study. It also

indicated that reflex alteration in pharyngeal musculature and biomechanical

conditions of supra and infrahyoid muscles occur postoperatively.

Taylor et al59

(1996) gave brilliant literature regarding the soft tissue growth of

oropharynx. With the help of lateral cephalograms, they demonstrated that hyoid

bone descends and moves slightly anterior upto age 18. The soft palate increased

1 mm in length and 0.5 mm in thickness every 3years after age 9. Thus, in

general, two periods of accelerated change (6-9 yrs. and 12-15 yrs.) and two

periods of quiescence (9-12 yrs. and 15-18 yrs.) were identified for pharyngeal

soft tissue.


14

Ioannis Kollias et al39

(1999) conducted a longitudinal study to investigate by

cephalometric means the alterations in craniofacial morphology and hyoid bone

positions in males and females in three different age groups with a ten year

interval. They concluded that the hyoid bone assumed a more inferior position

in adult life in relation to various skeletal structures in both men and women. In

males, the descent was more pronounced than that in females. The horizontal

position was however found to be stable.

Joanna M. battagel et al43

(2000) analyzed the upright lateral cephalometric

radiographs of 115 dentate Caucasian males. 45 subjects exhibiting proven

Obstructive Sleep Apnoea Syndrome, 45 simple snorers and remaining 24

subjects with no history of respiratory disease or snoring, acted as controls. Only

the cranial base angle and mandibular body showed significant intergroup

differences. Both snorers and OSAS patients exhibited narrow airway, reduced

oropharyngeal areas, shorter and thicker soft palate and large tongue than their

control counterparts.

Boon H.Seto et al12

(2001) tested the hypothesis that maxillary morphology

differs between OSAS patients and non-snoring, non-apnoea control subjects.

Patients had a smaller maxillary to mandibular and maxillary to facial width

ratios. These results suggest that OSA patients have narrower, more tapered and

shorter maxillary arches than the controls.


15

Armando Gale et al5 (2001) studied the hyoid bone position after surgical

mandibular advancement and concluded that with a surgical advancement of

the mandible the hyoid bone follows the advancement and moves closer to the

body of the mandible. However there are variations in the positions of the

hyoid bone and head position that are difficult to predict.

Anette M. C. Fransson et al3 (2002) in their study of influence of mandibular

protruding device on airway passages and dentofacial characteristics in

obstructive sleep apnoea and snoring evaluated the influence of a mandibular

protruding device (MPD) after 2 years of nocturnal usage on the upper airway

and its surrounding structures. They concluded that the nocturnal use of an MPD

for 2 years improved the airway passage because of an increase in the pharyngeal

area by a mean of 9% in OSA patients and snorers. A mandibular posterior

rotation and a proclination of the mandibular incisors were observed but

considered modest.

Takahashi.S and Ono.T et al79

(2002) conducted a study on breathing modes,

body positions, and suprahyoid muscle activity. Electromyographic activities of

genioglossus and geniohyoid muscles were recorded during both nasal and oral

breathing, with the subjects were in the both upright and supine positions. The

EMG activities of the genioglossus and geniohyoid muscles were compared

during mouth opening, swallowing, mandibular advancement, and tongue


16

protrusion. They concluded that EMG activities from the genioglossus and

geniohyoid muscles were differentiated well. Also, it appears that variations in

the breathing mode and body position significantly affect the genioglossus

activity and not that of the geniohyoid activity.

Lena Zettergren-Wijk et al50

(2002) evaluated longitudinal effect on facial

growth after tonsillectomy in children with obstructive sleep apnoea. They

studied 14 children with mean age of 5.7 years. Polysomnographic and lateral

cephalometric evaluation Preoperative, 1-year postoperative, and 3-year

postoperative revealed normalization of the facial growth after relief of the

obstruction (tonsillectomy) occurred mostly during the first postoperative year.

Siddik Malkoc, et al76

(2005) studied the Reproducibility of airway dimensions

and tongue and hyoid positions on lateral cephalograms. Three lateral

cephalograms each of 30 patients were obtained in natural head positions at 30-

minute intermissions. 12 measurements, including pharyngeal airway dimensions

and tongue and hyoid positions, were taken and analysed. They concluded that

airway dimension and tongue- and hyoid bone position measurements are highly

reproducible on natural-head-position cephalograms.


17

Mirja Kirjavainena & Turkka Kirjavainen61

(2007) studied the upper airway

dimensions in Class II malocclusion and effect of cervical headgear treatment on

it using lateral cephalograms. They concluded that Class II division 1

malocclusion is associated with narrower upper airway even without retrognathia.

Headgear treatment is associated with an increase in retropalatal airway space.

Craig Fairburn et al18

(2007) analysed the morphologic 3 dimensional changes

in the airway in OSA patients using CT scanning following maxillomandibular

advancement surgery. It resulted in a significant increase in both anteroposterior

and lateral airway dimensions.

Gunduz Arslan et al31

(2007) evaluated craniofacial and upper airway structures

in lateral cephalograms of patients with hypohydrotic ectodermal dysplasia,

whose characteristic features are Class III malocclusion with retrusion of maxilla,

and deficiency in vertical, transverse and sagittal growth of the jaw. Ectodermal

dysplasia patients have smaller pharyngeal and upper airway dimensions, and

hyoid bone is positioned more posteriorly compared with Class III control

individuals.

Maria Julia et al54

(2007) conducted a cephalometric assessment of the hyoid

bone position in Oral Breathing Children and concluded that the hyoid bone


18

keeps a stable position, probably in order to secure correct ratios in the airways,

and it does not depend on the respiratory pattern.

Yuko Shigeta et al86

(2008) examined the influence of age and gender on the

oropharynx configuration using the computed tomography measurements. They

concluded that the airway lengthens with aging specifically in males and

speculated that it becomes more collapsible. No significant relationship was

identified in females.

Dan Grauer et al19

(2009) assessed the differences in airway shape and volume

among subjects with various facial patterns, using CBCT. Both airway volume

and shape vary with different anteroposterior jaw relations; airway shape but not

volume differs with various vertical jaw relationships.

Tomonori Iwasaki et al80

(2009) evaluated the characteristic shape of

oropharyngeal airway in children with Class III malocclusion by cone beam

computed tomography (CBCT). The Class III malocclusion is associated with a

large and flat oropharyngeal airway compared with Class I malocclusion.

Emine Kaygısız et al23

(2009) appraised the effects of maxillary protraction and

fixed appliance therapy on the pharyngeal airway. 25 patients (11 girls, 14 boys;


19

mean age, 11.32 years) treated with a reverse pull headgear appliance were

assessed in their study. They concluded that the nasopharyngeal airway

dimensions improved after the treatment with maxillary protraction, and

favourable effects in pharyngeal airway remained over the post-treatment period

of 4 years.

Soonshin Hwang et al78

(2010) in their lateral cephalometric study assessed the

changes in hyoid, tongue, pharyngeal airway and head posture in patients who had

mandibular setback surgery by intraoral vertical ramus osteotomy. The hyoid and

tongue moved posteriorly after the setback but had a tendency to relapse back to

its original position. However, the final pharyngeal airway width remained

narrower even after long term observation period.

Zhe Zhong et al87

(2010) did a cephalometric 1comparison study of upper airway

among different sagittal and vertical facial morphologies in non-snoring children.

In normodivergent group, a tendency for reduced upper airway in inferior part

was found in Class III, I and Class II subgroups in that order; while in normal

sagittal pattern, the superior part of airway decreased with the increasing

mandibular plane angle. Thus, they concluded that sagittal and vertical skeletal

patterns may be contributory factors for variation in inferior and superior part of

upper airway, respectively.


20

Yoon-Ji Kim et al83

(2010) studied the three dimensional pharyngeal airway

volumes in healthy preadolescent children with different anteroposterior skeletal

patterns using CBCT. They compared the airway volume in children with a

retrognathic mandible and those with normal craniofacial growth, to study the

possible relationship among the studied cephalometric variables and airway

morphology. The mean total airway volume in retrognathic patients was

significantly smaller than that of normal skeletal relationship. However, the

difference in the volume of four sub regions of airway was not statistically

significant between the two groups.

Ashok Kumar Jena et al7 (2010) in their study of sagittal mandibular

development effects on the dimensions of the awake pharyngeal airway passage

concluded that sagittal mandibular development had significant effects on the

dimensions of the awake pharyngeal airway passage. The length of the soft

palate was smaller among subjects with mandibular prognathism than among

subjects with normal and retrognathic mandibles. The thickness of the soft

palate was greater among mandibular prognathic subjects than among subjects

with normal and retrognathic mandibles. Sagittal mandibular development had

a significant influence on the inclination of the soft palate. The dimensions of

the nasopharynx and hypopharynx were independent of sagittal mandibular

development. The depth of the oropharynx was greater among subjects with

mandibular prognathism than among subjects with normal and retrognathic

mandibles


21

Pirilä-Parkkinen.K et al66

(2010) in their study about Cephalometric evaluation

of children with nocturnal sleep-disordered breathing concluded that upper

airway resistance syndrome (UARS) and obstructive sleep apnoea (OSA) were

associated with decreased pharyngeal diameters at the levels of the adenoids

(PNS–ad1) and tip of the uvula (u1–u2), an increased diameter at the level of the

base of the tongue (rl1–rl2), a thicker soft palate, and anteriorly positioned maxilla

in relation to the cranial base. Lateral cephalograms may thus reveal important

predictors for sleep-disordered breathing (SDB) in children.

Kyung-Min Oh et al47

(2011) in their study of Three-dimensional analysis of

pharyngeal airway form in children with anteroposterior facial patterns

concluded that Children with Class II malocclusion have more backward

orientation and smaller volume of the pharyngeal airway than do children with

Class I and III malocclusion. Inclination of the oropharyngeal airway might be

a key factor in determining the form of the entire pharyngeal airway and is

related to head posture. In the skeletal Class II group, the average inclination of

Oropharyngeal airway was significantly larger and the Oropharyngeal airway in

the sagittal plane was shown as a more backward orientation to the FH plane.

Tomonori Iwasaki et al81

(2011) evaluated the upper airway obstruction in

dolichofacial and brachyfacial children with Class II malocclusion. The size of

the airway did not differ much between the two facial types. They developed a


22

fluid-mechanical stimulation system to detect the differences in airway

obstruction that were not apparent from other morphologic studies.

Gundega Jakobsone et al30

(2011) evaluated the effect of maxillary

advancement and impaction on the upper airway after bimaxillary surgery to

correct Class III malocclusion. They concluded that clinically significant

advancement (>2 mm) of the maxilla significantly increased the airway dimension

at the nasopharyngeal level and to some extent compensated for the effect of

mandibular setback at the hypopharyngeal level.

Derya Germec-Cakan et al22

(2011) compared the changes in Uvulo-

glossopharyngeal dimensions in non-extraction, extraction with minimum

anchorage and extraction with maximum anchorage. They concluded that superior

and middle airway size increased in subjects treated with extraction and minimum

anchorage. In patients treated non-extraction by air-rotor stripping, no significant

change was observed in airway dimensions. Middle and inferior airway size

narrowed in subjects treated with extraction and maximum anchorage.

Pirila-Parkkinen et al67

(2011) evaluated the validity of upper airway assessment

by comparing the capability of two-dimensional lateral cephalograms in

recognizing pharyngeal obstruction with that of the three-dimensional magnetic


23

resonance imaging and clinical observation of tonsillar size. The findings

confirmed that lateral cephalograms are a valid method for measuring dimensions

of nasopharyngeal and retropalatal region; and for evaluating oropharyngeal size,

clinical assessment of tonsillar size is a relatively reliable method.

Hakan El and Palomo32

(2011) evaluated the nasal passage and oropharyngeal

airway volumes of patients with different dentofacial skeletal patterns. The study

sample consisted of 140 patients which were divided into 3 groups according to

the ANB angle as Class I (1°≤ ANB ≤ 3

°), Class II (ANB > 3

°) and Class III (ANB

< 1°). The area of most constricted region at the base of the tongue had a high

potential of explaining the oropharyngeal airway volume; which was smaller for

Class II subjects when compared to Class I and Class III subjects. Mandibular

position with respect to cranial base had an effect on oropharyngeal airway

volume; but the only significant difference in nasopharyngeal volume was

between Class I and Class II groups, with a smaller volume observed in Class II

group.

Faruk Izzet Ucar and Tancan Uysal24

(2011) measured the oropharyngeal

airway dimensions in subjects with Class I malocclusion and different growth

patterns. 31 low angle, 40 high angle and 33 normal growth pattern cases with

Class I malocclusion were examined using lateral cephalometric radiographs.

Statistically significant differences were found in nasopharyngeal airway space,


24

palatal tongue space, and upper posterior airway space and tongue gap. No

significant orofacial airway differences were determined between low angle and

normal growth subjects. High angle subjects had larger tongue gap than those

with normal and low angle. Nasopharyngeal airway space and upper pharyngeal

airway space were larger and palatal tongue space was narrower in low angle than

high angle subjects.

Yoshihiko Takemoto et al84

(2011) evaluated the Pharyngeal airway in children

with prognathism and normal occlusion. 25 girls with prognathism and 15 girls

with normal occlusion were assessed in their study. They concluded that girls with

prognathic mandible had a significantly wider lower pharyngeal airway compared

with those with normal occlusion.

Austin Phoenix et al9 (2011) studied the changes in hyoid bone position

following rapid maxillary expansion in adolescents and noted that before

treatment, the hyoid to mandibular plane distance is greater in patients with

narrow maxillae requiring RME. They concluded that the hyoid to mandibular

plane distance significantly decreased post rapid maxillary expansion while the

tongue length remained unaffected. They suggested that RME treatment tends

to normalize hyoid bone position.


25

Ashok Kumar and Ritu Duggal6 (2011) studied the hyoid bone position in

subjects with different vertical jaw dysplasia and concluded that the

anteroposterior position of the hyoid bone was more forward in subjects with

short face syndrome. The vertical position of the hyoid bone was comparable

among subjects with different vertical jaw dysplasias. The axial inclination of

the hyoid bone closely followed the axial inclination of the mandible.

Qingzhu Wang, Peizeng Jia, Nina K. Anderson, Lin Wang and Jiuxiang

Lin70

(2012) in their study compared the Changes of pharyngeal airway size and

hyoid bone position following orthodontic treatment of Class I bimaxillary

protrusion concluded that following retraction of incisors, the velopharyngeal,

glossopharyngeal, and hypopharyngeal airway became narrower. The changes of

the pharyngeal airway size were no different between the hyperdivergent and non-

hyperdivergent groups. The hyoid bone tends to move in a posterior and inferior

direction. A significant relationship has been demonstrated between the reduction

of the velopharynx, glossopharynx, and the retraction distance of lower incisors in

their study.

Fitin Aloufi et al25

(2012) in their retrospective study about the changes in the

upper and lower pharyngeal airway spaces associated with rapid maxillary

expansion concluded that rapid maxillary expansion during orthodontic

treatment have a positive effect on the upper nasopharyngeal airway, with no


26

significant change on the lower pharyngeal airway. They also confirmed that

there was no significant difference with respect to mode of breathing.

Nanda Kishore Sahoo et al63

(2012) evaluated the upper airway dimensional

changes and hyoid position following mandibular advancement in patients with

skeletal Class II malocclusion. They quantified upper airway dimensional changes

and hyoid bone positional variation for a given degree of mandibular

advancement. They established a ratio of mandibular advancement to increase in

airway dimensions. The mean ratio of mandibular advancement to increase

Posterior Airway Space, Superior Airway Space, and Minimum Airway Space

was 1:0.35, 1:0.34, and 1:0.24, respectively. Hyoid bone moved superiorly and in

an anterior direction by 2.1 ± 2.8 mm.

Yu Chen et al85

(2012) evaluated the effect of large incisor retraction on upper

airway morphology in adult bimaxillary protrusion patients using three-

dimensional multi slice computed tomography. 30 adult patients with bimaxillary

protrusion treated with four first premolars extractions and miniscrews anchorage

were evaluated. They concluded that the hyoid was retracted in the horizontal and

vertical directions. No significant difference was observed in the cross-sectional

area of the nasopharynx, while significant differences were found in the mean

cross-sectional areas of the glossopharynx, palatopharynx and hypopharynx these


27

mean cross-sectional areas were decreased. The largest change in the cross-

sectional area is always noted in the hypopharynx.

Sila Mermut Gokce et al77

(2012) studied the relationship between Class III

malocclusion and hyoid bone displacement during swallowing by using

cinemagnetic resonance imaging and concluded that the forward and upward

displacements of the hyoid bone during bolus swallowing were significantly

related to craniofacial morphology. Although the pattern of hyoid bone movement

during swallowing was similar in patients with skeletal Class III malocclusion and

control subjects with normal occlusion, differences were noted in the degree of the

movement. Specifically, as the magnitude of the skeletal Class III deformity

increased, the amount of forward and upward displacement of the Hyoid bone

increased.

Halise Aydemir et al33

(2012) in their study of Pharyngeal airway space, hyoid

bone position and head posture after orthognathic surgery in Class III patients

concluded that different surgical procedures have different effects on pharyngeal

airway space. Mandibular setback surgeries cause the most narrowing effect on

the pharyngeal airway. Bimaxillary surgeries mostly decrease the narrowing effect

of the mandibular setback surgeries and must be preferred when planning these

cases. Maxillary advancement procedures have a widening effect on the

pharyngeal airway. No significant change occurs in craniocervical posture and

hyoid bone position after Class III orthognathic surgeries.

Materials and Methods

28

Materials and methods

In this study, the treatment records of 40 patients who underwent fixed

orthodontic treatment between the years 2006 to 2009 at Department Of

Orthodontics and Dentofacial Orthopaedics, Tamilnadu Government Dental

College and Hospital Chennai were analysed. Of 40 sets of standardized lateral

cephalometric radiographs 20 were Class I malocclusion and 20 were Class II

malocclusion. The control group consisting of 20 lateral cephalograms of subjects

with normal occlusion and good visibility of hyoid bone were used. The age range

was between 18 and 25 years. Inclusion and exclusion criteria were analysed from

the clinical records of the subjects.

Selection criteria:

The lateral cephalograms evaluated for this study were taken in natural head

position, with PLANMECA PM 2002 CC PROLINE machine 70kvp, 30mA, for

1.8seconds from fixed distance of 60 inches from the cephalostat available in the

Department Of Oral Medicine and Radiology, Tamilnadu Government Dental

College and Hospital Chennai. All cephalograms were taken in same cephalostat

with Frankfort horizontal plane of the subjects parallel to the floor. All

cephalograms were standardized using a transparent grid of 1mm accuracy and

Adobe Photoshop CS5. All the radiographs were scanned with CANON D520 MF

scanner and digitized. A Cephalometric analysis software AX CEPH version

2.3.0.74 was used to analyse the radiographs.


29

Inclusion criteria for Class I group:

Skeletal Class I (ANB 2º- 4º), Class I molar and canine relationship.

Both maxillary and mandibular arches with moderate to severe crowding 69

(4-10

mm - moderate to severe crowding according to Little’s irregularity index)

Orthodontic treatment with extraction of four first premolars.

Average BMI and Growth pattern.

No obvious hyperplasia of tonsils or adenoids on cephalograms.

Pretreatment and posttreatment radiographs with good soft and hard tissue outlines

with good visibility of the hyoid bone and teeth in full occlusion, lips resting in

natural position.

Inclusion criteria for Class II group:

Mild to moderate skeletal Class II (ANB 5º-7º), Class II molar and canine

relationship.

Both maxillary and mandibular arches with moderate to severe crowding 69

(4-10

mm – moderate to severe crowding according to Little’s irregularity index)

Orthodontic treatment with extraction of two first premolars in upper arch & two

second premolars in lower arch.

Average BMI and Growth pattern.

No obvious hyperplasia of tonsils or adenoids and tongue on cephalograms.


30

Pretreatment and posttreatment cephalograms with good soft and hard tissue with

good visibility of the hyoid bone outlines and teeth in full occlusion, lips resting in

natural position.

Exclusion criteria:

Craniofacial anomalies.

History of craniofacial trauma & pathology.

History of previous craniofacial surgery / orthodontic treatment.

History of abnormal oral habits.

History of nasal obstruction and allergic conditions.

Cephalometric evaluation:

The pharynx is divided into of four different sections, nasopharynx, velopharynx,

glossopharynx, and hypopharynx. 7 parameters for these 4 sections of pharynx and

4 parameters for hyoid bone positions were selected and analysed 70

.

Cephalometric Landmarks and Measurements Analysed :

Table 1 : Cephalometric landmarks

Hor Most inferior point of spheno-occipital synchondrosis

R

Point of intersection of line from Hor to PNS and posterior

pharyngeal wall

Ba Lowermost point on anterior margin of foramen magnum

Ad1 Point of intersection of posterior pharyngeal wall and line Ptm-Ba


31

SPPW

Point of intersection of line from soft palate center perpendicular to

posterior pharyngeal wall and posterior pharyngeal wall

SPP

Point of intersection of line from soft palate center perpendicular to

posterior pharyngeal wall and posterior margin of soft palate

U The tip of the uvula

MPW

Foot point of perpendicular line from point U to posterior

pharyngeal wall

TPPW

Point of intersection of posterior pharyngeal wall and

extension of line B-Go

V The most posteroinferior point on the base of the tongue

TB

Point of intersection of base of the tongue & extension of

line B-Go

LPW

Foot point of perpendicular line from point V to posterior

pharyngeal wall

E Base of epiglottis.

C3 The most anteroinferior point of the third vertebra

H The most superior and anterior point of hyoid bone

RGN The most protrusive point of retrognathion

H1 Foot point of perpendicular line from RGN to C3


32

Table 2 :Airway Parameters (in mm)

VAL

Vertical airway length, distance

between PNS and V

PNS-R Distance between PNS and R.

PNS-Ad1 Distance between PNS and Ad1.

SPP-SPPW Distance between SPP and SPPW.

U-MPW Distance between U and MPW.

TB-TPPW Distance between TB and TPPW.

U-MPW Distance between U and MPW.

TB-TPPW Distance between TB and TPPW.

V-LPW Distance between V and LPW.

Table 3: Hyoid Position Parameters (in mm)

HRgn , mm Distance between H and RGN

HH1, mm Distance between H and H1

C3H, mm Distance between C3 and H

SH, mm Distance between S and H

Table 4 :Dentofacial Parameters

ANB, degrees Angle between point A and B at nasion

FH-MP, degrees Angle between the mandibular plane and the FH plane

U1-FH, degrees Angle between the FH plane & long axis of upper incisors

L1-MP, degrees Angle between the mandibular plane and long axis of lower


33

incisors

UL-E line, mm

Horizontal distance from the most protrusive point of upper

lip to E line

LL-E line, mm

Horizontal distance from the most protrusive point of lower

lip to E line

U1FHp, mm

Horizontal distance from the tip of the upper incisor crown to

constructed FH plane vertical

L1FHp, mm

Horizontal distance from the tip of the lower incisor crown to

constructed FH plane vertical

U6FHp, mm

Horizontal distance from the distal point of the upper first

molar crown to constructed FH plane vertical

L6FHp, mm

Horizontal distance from the distal point of the lower first

molar crown to constructed FH plane vertical

The process of digitization, landmark identification and analysis for all

cephalograms were carried out by same investigator. The intra-examiner reliability

was evaluated by re-recording the measurements at three weeks interval.


34

Cephalostat

CANON D520 MF scanner


35

Standardization with Transparent Grid

Standardization with Adobe Photoshop CS5


36

Ax Ceph Cephalometric Analysis Software

Analysis of digitized lateral cephalograms – Control subject


37

Analysis of digitized lateral cephalograms of Class I subject - pretreatment

Analysis of digitized lateral cephalograms of Class I subject - posttreatment


38

Analysis of digitized lateral cephalograms of Class II subject - pretreatment

Analysis of digitized lateral cephalograms of Class II subject - posttreatment

Statistical Analysis

39

Statistical Analysis

The data collected during the study was recorded in Microsoft Excel

Spreadsheet. The data was subjected to data analysis using Statistical Package for

Social Sciences (SPSS) software version 17. Within group differences in data

pertaining to airway dimension parameters, hyoid bone position parameters and

Dentofacial parameters among Class I and Class II malocclusion group before and

after treatment was compared using paired t test. Between group differences in the

above parameters among subjects with ideal group, Class I group and Class II

group was compared using one way ANOVA.

The intra-examiner reliability in recording the measurements was assessed

using Cronbach’s alpha method.

For all the analysis, p value of < 0.05 was considered to be statistically

significant.

Results

40

RESULTS

Table 5: Distribution of study subjects based on their gender

Gender Normoocclusion

(n) Class I group (n) Class II group (n)

Male 10 9 12

Female 10 11 8

Chi square value – 0.93 df – 2 p value - 0.62 (NS)

10

9

12

10

11

8

0

2

4

6

8

10

12

14

Normoocllusion (n) Class I (n) Class II (n)

male

female

Nu

mb

er o

f su

bje

cts

Results

41

Table 6: Distribution of study subjects based on their age

Type of occlusion Mean age S.D F value p value

Normoocclusion 21.2 1.92

2.74 0.07 (NS) Class I group 21.4 1.81

Class II group 21.05 1.76

The intra-examiner reliability was evaluated by re-recording the

measurements at three weeks interval. The kappa value for reliability was found

to be 0.84 denoting a high level of consistency in recording the measurements at

two different time period.

20.8

20.9

21

21.1

21.2

21.3

21.4

Normoocclusion CLASS I CLASS II

Age

Results

42

Table 7: Comparison of Airway related parameters among study subjects within

Class I malocclusion group

Variable Mean Std.

Devn

Mean

difference t value df

p

value

PNS –R

(mm)

Pre-treatment 22.36 1.66 -0.20 -3.27 19 0.004

Post-treatment 22.55 1.65

PNS -Ad1

(mm)

Pre-treatment 31.45 1.21 0.26 3.69 19 0.002


SPP-

SPPW

(mm)

Pre-treatment 17.95 1.00 0.36 4.07 19 0.001


U-MPW

(mm)

Pre-treatment 11.39 0.97 0.60 3.33 19 0.004


TB-

TPPW

(mm)

Pre-treatment 10.85 0.95 0.73 5.91 19 0.001


V-LPW

(mm)

Pre-treatment 14.08 1.37 1.14 14.44 19 0.001


VAL

(mm)

Pre-treatment 60.72 1.39 -0.95 -6.42 19 0.001


Table 8: Comparison of Hyoid position related parameters among study subjects


Variable Mean Std.

Devn

Mean

difference t value df p value

HRGN

(mm)

Pre-treatment 34.30 1.27 -1.04 -6.46 19 0.001


HH1

(mm)

Pre-treatment 3.58 0.81 -0.38 -2.28 19 0.035


C3H

(mm)

Pre-treatment 38.18 1.25 0.89 7.68 19 0.001


SH

(mm)

Pre-treatment 91.74 3.13 -1.30 -9.40 19 0.001


Results

43

Table 9: Comparison of Dento-facial related parameters among study subjects


Variable Mean Std.

Deviation

Mean

difference t value df

p

value

ANB

(degree)

Pre-treatment 3.11 0.71 -0.11 -1.67 19 0.112


FH-MP

(degree)

Pre-treatment 25.27 2.11 -0.37 -4.72 19 0.001


U1-FH

(degree)

Pre-treatment 128.64 4.41 14.92 38.16 19 0.001


L1-MP

(degree)

Pre-treatment 100.50 4.30 6.51 21.77 19 0.001


UL-Eline

(mm)

Pre-treatment 3.23 1.18 2.13 11.37 19 0.001


LL-Eline

(mm)

Pre-treatment 5.28 0.84 3.24 22.19 19 0.001


U1-FHP

(mm)

Pre-treatment 79.19 2.62 6.26 25.76 19 0.001


L1-FHP

(mm)

Pre-treatment 75.27 2.28 4.70 24.47 19 0.001


U6-FHP

(mm)

Pre-treatment 40.11 1.40 -0.60 -7.78 19 0.001


L6-FHP

(mm)

Pre-treatment 40.55 1.40 -0.62 -8.57 19 0.001


Results

44

Table 10: Comparison of Airway related parameters among study subjects within

Class II malocclusion group

Table 11: Comparison of Hyoid position parameters among study subjects within

Class II malocclusion group

Variable Mean Std.

Devn

Mean


HRGN

(mm)

Pre-treatment 36.41 2.59 .38 14.90 19 0.001


HH1

(mm)

Pre-treatment 2.73 .81 .49 8.67 19 0.001

Post-treatment 2.24 .79

C3H

(mm)

Pre-treatment 34.79 2.37 -.94 -10.98 19 0.001


SH

(mm)

Pre-treatment 93.85 3.64 1.19 6.72 19 0.001


Variable Mean Std.

Devn

Mean


PNS –R

(mm)

Pre-treatment 25.45 1.34 .46 3.63 19 .002


PNS -Ad1

(mm)

Pre-treatment 34.55 1.36 .78 3.47 19 .003


SPP-SPPW

(mm)

Pre-treatment 16.48 1.24 -.09 -.73 19 .476


U-MPW

(mm)

Pre-treatment 13.85 1.04 -1.05 -12.46 19 0.001


TB-TPPW

(mm)

Pre-treatment 11.06 1.23 -1.29 -14.23 19 0.001


V-LPW

(mm)

Pre-treatment 11.03 1.32 -2.31 -21.59 19 0.001


VAL

(mm)

Pre-treatment 55.95 2.20 -1.31 -8.29 19 0.001


Results

45

Table 12: Comparison of Dento facial related parameters among study subjects

within Class II malocclusion group

variable Mean Std.

Devn

Mean


ANB

(degree)

Pre-treatment 5.98 .79

.67 11.05 19 0.001


FH-MP

(degree)

Pre-treatment 26.03 1.59

-.75 -8.20 19 0.001


U1-FH

(degree)


11.72 22.21 19 0.001


L1-MP

(degree)


7.45 13.29 19 0.001


UL-Eline

(mm)


2.66 12.83 19 0.001


LL-Eline

(mm)

Pre-treatment 5.36 .81

3.34 27.10 19 0.001


U1-FHP

(mm)


5.25 29.13 19 0.001


L1-FHP

(mm)


3.09 21.21 19 0.001


U6-FHP

(mm)


-.64 -5.61 19 0.001


L6-FHP

(mm)


-3.23 -14.13 19 0.001


Results

46

TABLE 13: Comparison of airway parameters between Class I and Class II

malocclusion groups

Class N Mean Std. Devn

Std. Error

Mean

PNS-R

PRE

Class 1 20 22.3560 1.66376 .37203

Class 2 20 25.4455 1.33739 .29905

PNS-R

POST

Class 1 20 22.554 1.6472 .3683

Class 2 20 24.987 1.3848 .3096

PNS-AD1

PRE

Class 1 20 31.4545 1.21288 .27121

Class 2 20 34.5525 1.36179 .30451

PNS-AD1

POST

Class 1 20 31.198 1.3254 .2964

Class 2 20 33.775 1.8265 .4084

SPP-SPPW

PRE

Class 1 20 17.9450 1.00384 .22447

Class 2 20 16.4785 1.23577 .27633

SPP-SPPW

POST

Class 1 20 17.5810 1.09900 .24574

Class 2 20 16.5680 1.15832 .25901

U-MPW

PRE

Class 1 20 11.3905 .96696 .21622

Class 2 20 13.8520 1.04164 .23292

U-MPW

POST

Class 1 20 10.7900 1.21063 .27071

Class 2 20 14.9055 1.06762 .23873

TB – TPPW

PRE

Class 1 20 10.8480 .95446 .21342

Class 2 20 11.0585 1.22819 .27463

TB – TPPW

POST

Class 1 20 10.1220 .95095 .21264

Class 2 20 12.3500 1.05607 .23614

V-LPW

PRE

Class 1 20 14.0780 1.37332 .30708

Class 2 20 11.0280 1.31877 .29489

V-LPW

POST

Class 1 20 12.9340 1.41081 .31547

Class 2 20 13.3425 1.31865 .29486

VAL

PRE

Class 1 20 60.716 1.3861 .3100

Class 2 20 55.946 2.1985 .4916

VAL

POST

Class 1 20 61.666 1.3455 .3009

Class 2 20 57.257 2.4904 .5559

Results

47

Table 14: Comparison of Airway Parameters between Class I And Class II

Malocclusion Groups - Independent Samples Test

Levene's

test

for

Equality

of

Variances

t-test for Equality of Means

F Sig. t df

Sig.

(2-

tailed)

Mean

Difference

Std. Error

Difference

PNS-R

PRE

Equal

variances

assumed

.927 .342 -6.473 38 <.001 -3.0895 .47732

Equal

variances not

assumed

-6.473 36.322 <.001 -3.0895 .47732

PNS-R

POST

Equal

variances

assumed

.757 .390 -5.055 38 <.001 -2.432 .4812

Equal

variances not

assumed

-5.055 36.910 <.001 -2.432 .4812

PNS-

AD1

PRE

Equal

variances

assumed

.875 .355 -7.597 38 <.001 -3.0980 .40777

Equal

variances not

assumed

-7.597 37.502 <.001 -3.0980 .40777

PNS-

AD1

POST

Equal

variances

assumed

3.607 .065 -5.107 38 <.001 -2.577 .5046

Equal

variances not

assumed

-5.107 34.666 <.001 -2.577 .5046

SPP-

SPPW

PRE

Equal

variances

assumed

.776 .384 4.119 38 <.001 1.4665 .35601

Equal

variances not

assumed

4.119 36.469 <.001 1.4665 .35601

SPP-

SPPW

POST

Equal

variances

assumed

.007 .936 2.837 38 .007 1.0130 .35704

Equal

variances not

assumed

2.837 37.895 .007 1.0130 .35704

U-

MPW

PRE

Equal

variances

assumed

.223 .640 -7.745 38 <.001 -2.4615 .31781

Equal

variances not

assumed

-7.745 37.792 <.001 -2.4615 .31781

Results

48

U-

MPW

POST

Equal

variances

assumed

.001 .982 -

11.402 38 <.001 -4.1155 .36093

Equal

variances not

assumed

-

11.402 37.415 <.001 -4.1155 .36093

TB –

TPPW

PRE

Equal

variances

assumed

1.350 .253 -.605 38 .549 -.2105 .34781

Equal

variances not

assumed

-.605 35.816 .549 -.2105 .34781

TB –

TPPW

POST

Equal

variances

assumed

1.214 .277 -7.011 38 <.001 -2.2280 .31777

Equal

variances not

assumed

-7.011 37.590 <.001 -2.2280 .31777

V-

LPW

PRE

Equal

variances

assumed

.053 .820 7.164 38 <.001 3.0500 .42574

Equal

variances not

assumed

7.164 37.938 <.001 3.0500 .42574

V-

LPW

POST

Equal

variances

assumed

.271 .605 -.946 38 .350 -.4085 .43181

Equal

variances not

assumed

-.946 37.828 .350 -.4085 .43181

VAL

PRE

Equal

variances

assumed

5.365 .026 8.206 38 <.001 4.769 .5812

Equal

variances not

assumed

8.206 32.045 <.001 4.769 .5812

VAL

POST

Equal

variances

assumed

5.890 .020 6.966 38 <.001 4.409 .6329

Equal

variances not

assumed

6.966 29.222 <.001 4.409 .6329

Results

49

Table 15: Comparison of hyoid position related parameters between Class I and

Class II malocclusion groups.

Class N Mean Std. Deviation Std. Error

Mean

H-RGN

PRE

Class 1 20 34.2990 1.26646 .28319

Class 2 20 36.4110 2.59176 .57954

H-RGN

POST

Class 1 20 35.3360 1.31194 .29336

Class 2 20 36.0305 2.58043 .57700

HH1

PRE

Class 1 20 3.5775 .80951 .18101

Class 2 20 2.7280 .80983 .18108

HH1

POST

Class 1 20 3.9525 .69208 .15475

Class 2 20 2.2400 .79382 .17750

C3H

PRE

Class 1 20 38.1810 1.25319 .28022

Class 2 20 34.7930 2.36943 .52982

C3H

POST

Class 1 20 37.288 1.1603 .2594

Class 2 20 35.733 2.3734 .5307

SH

PRE

Class 1 20 91.7360 3.13418 .70082

Class 2 20 93.8490 3.64104 .81416

SH

POST

Class 1 20 93.037 2.8947 .6473

Class 2 20 92.664 3.7273 .8335

Table 16: Comparison of hyoid position related parameters between subjects with

Class I and Class II occlusion - Independent Samples Test

Levene's Test

for Equality

of Variances


F Sig. t df Sig.(2-

tailed)

Mean

Difference

Std. Error

Difference

H-

RGN

PRE

Equal

variances

assumed

14.986 .000 -

3.274 38 .002 -2.1120 .64502

Equal

variances not

assumed

-

3.274 27.584 .003 -2.1120 .64502

H-

RGN

POST

Equal

variances

assumed

14.247 .001 -

1.073 38 .290 -.6945 .64729

Equal

variances not

-

1.073 28.207 .292 -.6945 .64729

Results

50

assumed

HH1

PRE

Equal

variances

assumed

.014 .908 3.318 38 .002 .8495 .25604

Equal

variances not

assumed

3.318 38.000 .002 .8495 .25604

HH1

POST

Equal

variances

assumed

.357 .553 7.272 38 <.001 1.7125 .23549

Equal

variances not

assumed

7.272 37.307 <.001 1.7125 .23549

C3H

PRE

Equal

variances

assumed

8.663 .006 5.653 38 <.001 3.3880 .59936

Equal

variances not

assumed

5.653 28.859 <.001 3.3880 .59936

C3H

POST

Equal

variances

assumed

8.561 .006 2.631 38 .012 1.555 .5907

Equal

variances not

assumed

2.631 27.591 .014 1.555 .5907

SH

PRE

Equal

variances

assumed

.121 .730 -

1.967 38 .057 -2.1130 1.07425

Equal

variances not

assumed

-

1.967 37.177 .057 -2.1130 1.07425

SH

POST

Equal

variances

assumed

1.002 .323 .353 38 .726 .373 1.0553

Equal

variances not

assumed

.353 35.806 .726 .373 1.0553

Results

51

Table 17: Comparison of airway related parameters between subjects

with Normal, Class I and Class II occlusion at baseline (mm)

Variable Normal

subjects

Class I

subjects

Class II

subjects F value* p value

PNS –R

(mm) 22.6 22.36 25.45 15.17 < 0.001

PNS -Ad1

(mm) 28.61 31.45 34.55 37.11 < 0.001

SPP-SPPW

(mm) 15.95 17.95 16.48 3.72 0.03

U-MPW

(mm) 10.78 11.39 13.85 34.10 < 0.001

TB-TPPW

(mm) 10.34 10.85 11.06 0.85 0.43

V-LPW

(mm) 15.11 14.08 11.03 25.5 < 0.001

VAL

(mm) 59.54 60.72 55.95 12.91 < 0.001

*One way ANOVA

Table 18: Comparison of airway related parameters between subjects

with Normal, Class I and Class II occlusion post treatment (mm)

Variable Normal subjects

Class I

subjects

Class II

subjects

F value* p value

PNS –R

(mm) 22.6 22.55 24.99 9.92 < 0.001

PNS -Ad1

(mm) 28.61 31.2 33.78 24.94 < 0.001

SPP-SPPW

(mm) 15.95 17.58 16.57 2.34 0.104

U-MPW

(mm) 10.78 10.79 14.91 65.02 < 0.001

TB-TPPW

(mm) 10.34 10.12 12.35 9.78 < 0.001

V-LPW

(mm) 15.11 12.93 13.34 7.52 0.001

VAL

(mm) 59.54 61.67 57.26 9.75 < 0.001

*One way ANOVA

Results

52

Table 19: Comparison of hyoid position related parameters between

subjects with Normal, Class I and Class II occlusion baseline (mm)

Variable Normal

subjects

Class I

subjects

Class II

subjects F value* p value

HRGN

(mm) 36.95 34.30 36.41 3.05 0.05

HH1 (mm) 3.16 3.58 2.73 0.75 0.47

C3H (mm) 39.00 38.18 34.79 8.22 < 0.001

SH (mm) 97.23 91.74 93.85 5.85 0.004

*One way ANOVA

Table20: Comparison of hyoid position related parameters between

subjects with Normal, Class I and Class II occlusion post treatment

(mm)

Variable Normal

subjects

Class I

subjects

Class II

subjects

F

value*

p

value

Mean HRGN

(mm) 36.95 35.34 36.03 1.01 0.36

Mean HH1 (mm) 3.16 3.95 2.24 3.12 0.05

Mean C3H (mm) 39.00 37.29 35.73 4.44 0.01

Mean SH (mm) 97.23 93.04 92.66 4.96 0.01

*One way ANOVA

Results

53

Table 21– Changes In Airway dimension And Hyoid bone position – Based On

Gender

Levene's

Test for

Equality of

Variances


F Sig. t df

Sig.

(2-

tailed)

Mean

Difference

Std. Error

Differenc

e

Pns-R

pre

Equal variances

assumed 3.561 .075 -.164 18 .871 -.1261 .76772

Equal variances

not assumed -.174 15.970 .864 -.1261 .72524

Pns-R

post

Equal variances

assumed 3.899 .064 -.040 18 .969 -.030 .7606

Equal variances

not assumed -.042 15.818 .967 -.030 .7175

Pns-Ad1

Pre

Equal variances

assumed 1.348 .261 .220 18 .828 .1231 .55934

Equal variances

not assumed .215 15.078 .833 .1231 .57335

Pns Ad1

Post

Equal variances

assumed 2.126 .162 .016 18 .988 .010 .6120

Equal variances

not assumed .015 13.513 .988 .010 .6371

SPP-

SPPW

Pre

Equal variances

assumed .423 .524 .365 18 .719 .1687 .46185

Equal variances

not assumed .358 15.609 .725 .1687 .47086

SPP-

SPPW

Post

Equal variances

assumed .577 .457 -.039 18 .969 -.0200 .50748

Equal variances

not assumed -.039 15.847 .970 -.0200 .51609

U-MPW

Pre

Equal variances

assumed .449 .511 -.457 18 .653 -.2029 .44395

Equal variances

not assumed -.456 17.002 .654 -.2029 .44537

U-MPW

Post

Equal variances

assumed 3.864 .065 -1.296 18 .211 -.6929 .53466

Equal variances

not assumed -1.215 11.139 .250 -.6929 .57037

TB-

TPPW

Pre

Equal variances

assumed .962 .340 .293 18 .773 .1289 .43971

Equal variances

not assumed .301 17.942 .767 .1289 .42767

TB-

TPPW

Post

Equal variances

assumed .482 .497 .167 18 .869 .0731 .43879

Results

54

Equal variances

not assumed .161 14.297 .874 .0731 .45327

V-LPW

Pre

Equal variances

assumed .114 .739 .683 18 .503 .4279 .62611

Equal variances

not assumed .681 16.995 .505 .4279 .62815

V-LPW

Post

Equal variances

assumed .700 .414 .680 18 .505 .4372 .64329

Equal variances

not assumed .685 17.675 .502 .4372 .63811

VAL

pre

Equal variances

assumed .040 .843 .190 18 .852 .121 .6395

Equal variances

not assumed .192 17.889 .850 .121 .6306

VAL

Post

Equal variances

assumed 1.491 .238 .752 18 .462 .460 .6118

Equal variances

not assumed .729 14.553 .477 .460 .6304

H-RGN

Pre

Equal variances

assumed 1.250 .278 -.350 18 .730 -.2042 .58284

Equal variances

not assumed -.334 12.860 .743 -.2042 .61064

H-RGN

post

Equal variances

assumed .404 .533 .380 18 .708 .2295 .60341

Equal variances

not assumed .374 15.862 .713 .2295 .61356

HH1

pre

Equal variances

assumed .536 .474 -.756 18 .459 -.2783 .36802

Equal variances

not assumed -.761 17.579 .457 -.2783 .36579

HH1

Post

Equal variances

assumed 1.801 .196 -1.875 18 .077 -.5480 .29233

Equal variances

not assumed -1.947 17.563 .068 -.5480 .28150

C3H

pre

Equal variances

assumed .041 .843 -.248 18 .807 -.1432 .57772

Equal variances

not assumed -.248 17.147 .807 -.1432 .57837

C3H

Post

Equal variances

assumed .028 .869 -.797 18 .436 -.420 .5266

Equal variances

not assumed -.802 17.602 .433 -.420 .5232

SH

pr

Equal variances

assumed 1.725 .206 -.588 18 .564 -.8432 1.43360

Equal variances

not assumed -.571 14.667 .576 -.8432 1.47551

SH

post

Equal variances

assumed 2.796 .112 -.532 18 .601 -.706 1.3264

Equal variances

not assumed -.507 12.719 .621 -.706 1.3916

Discussion

55

Discussion

Pharyngeal airway dimensions, narrowing of pharyngeal passage and

hyoid bone positions are of interest in orthodontics. Several studies have

indicated that there are significant relationships between pharyngeal

dimensions and craniofacial abnormalities.

Nasopharyngeal airway area increases rapidly until 13 years of age and

after this the growth slows down. An inactive period of growth in pharyngeal

structures has been reported beyond 15 years of age.16,82,42,51,59

. Chang min et

al 15

reported the developmental changes on pharynx and hyoid position. By 3

years of age the hyoid lies at a level between 3rd and 4th cervical vertebrae and

descends to the level of the 4th vertebrae at adulthood. Later during growth the

relative position of the hyoid remains constant.14,74

. Literature findings indicate

that growth may have little effect if any on the sagittal depth of the pharyngeal

airway.

This study was performed to evaluate the changes in the pharyngeal

airway dimensions and the hyoid bone position following nonsurgical

orthodontic treatment in class I and class II subjects with moderate to severe

crowding and compared with normoocclusion using lateral cephalometric

radiograph. In the present study subjects of 18 – 25 years of age were

evaluated.

As this analytical study was retrospective in nature, direct assessment of

the respiratory pattern for individual patient was not possible. The medical

Discussion

56

history and dental history recorded in the clinical orthodontic records were

analysed for the criteria for selection of the subjects. Prior history about

tonsillectomy and respiratory infections were considered. Any one of these

factors could have been related to respiratory obstructions 44, 62

. Patients with a

positive history of airway obstructions and other craniofacial abnormalities

were excluded from the study. All the subjects in this study had normal BMI

and were treated with extractions followed by straight wire appliance 0.022”

Roth prescription.

Husamettin Oktay 36

and Hiroyuki Ishikawa et al 35

reported that ANB

angle was considered to be the reliable indicator of the anteroposterior skeletal

discrepancy. Although clinical significance and reliability of the ANB angle to

determine the anteroposterior jaw relationship was argued in the literature, it is

still a widely used method to describe anteroposterior dentofacial discrepancies

and thus was the measurement of choice for this study to group the subjects. In

our study, subjects with ANB angle between 2-4º were included in Class I

group and subjects with ANB angle 5-7º were included in Class II group.

Normal respiration is dependent on sufficient anatomical dimensions of

the airway. Many studies have contributed to the knowledge that variations in

the skeletal pattern could lead to upper airway obstruction.55

The pharyngeal airway is an irregular lumen. Narrowing in one or more

segments of the airway may induce breathing as well as sleeping problems like

obstructive apnoea. Cross sectional area is a better indicator than volume with

Discussion

57

which to evaluate change in the size of the pharyngeal airway. The size of the

pharyngeal airway on lateral cephalograms can be measured as the depth and

height in the sagittal plane. So there is an inherent limitation of the study as

pharyngeal airway is a three-dimensional structure and it can only be evaluated

two dimensionally on lateral cephalometric films. However, Miles et al.

reported a high reliability of cephalometric landmarks and measurements 60

.

Aboudara et al 13

showed that the resistance to airflow is related to

airway size as well as form. So if the airway has a large volume but is bent,

then the airway resistance could greatly affect respiration. An airflow test,

nasoendoscope examination, nasal resistance measures, lateral cephalograms ,

Magnetic Resonance Imaging, Computed tomography, Cone Beam CT are

used for diagnosing nasal obstruction. Lateral cephalograms particularly have

been a very helpful tool because of their simplicity, low cost, and

reproducibility13, 67

. In our study, lateral cephalograms were used to analyse the

pharyngeal airway dimension and hyoid bone positions.

The process of converting the analogue information into digital form is

called digitization. Quantitative, systematic, and objective measurements based

on hard and soft tissue landmarks determined on cephalometric films are used

in orthodontics as a valuable tool in orthodontics. Korkmaz Sayinsu et al 46

and

Cleomar Donizeth Rodrigues et al 17

confirmed that there was no statistically as

well as clinically significant difference in the tracings between digitized

cephalograms, direct digital and conventional methods. In the present study

Discussion

58

lateral cephalograms were digitized using Canon D520 Mf scanner and

analysed using Ax Ceph version 2.3.0.74 software.

Mergen D.C and Jacobs R.M20

in their study measured the size of

nasopharynx (upper pharyngeal airway); and compared it between those with

normal Class I occlusion and Class II malocclusion. They concluded that the

midsagittal nasopharyngeal area was significantly greater in subjects with

normal class I occlusion than in those with Class II malocclusion. Oscar Martin

et al65

tried to describe the nasopharyngeal patterns in patients with ideal

occlusions and found that nasal fossa, cranial base, and adenoid tissue were

larger in men than in women. However, Marcos Roberto de Freitas et al53

did

not find any correlation between the upper pharyngeal airway in Class I and

Class II malocclusion types; but concluded that those with vertical growth

pattern have narrower upper airway dimensions.

In this pharyngeal dimension study, Class I and Class II malocclusion

(skeletal and dental) subjects with crowding grades from 4 to 10 mm69

analysed

from the models (Little’s irregularity index – moderate to severe) were

included and compared with normoocclusion subjects.

All subjects in this group were treated with extraction of four first

premolars. In class II group all subjects were treated with extraction of two

maxillary first premolars and two mandibular second premolars .The extraction

space was utilized for correction of crowding and mild proclination.

Discussion

59

A significant correlation was observed among the extent of central

incisor retraction, the amount of hyoid retraction in the horizontal direction,

and the change in the cross-sectional area of the hypopharynx85

. The main

reason for the narrowing of the hypopharynx may be the retraction of the

hyoid, which was caused by the retraction of the central incisor. Previous

studies have shown a possible relationship between hypopharynx and skeletal

structures, soft tissues, and musculature.55, 78

.

In the present study, changes in the nasopharynx, velopharynx,

glossopharynx and hypopharynx dimensions and hyoid bone positions were

measured according to the methods followed by Zhe zhong et al 87

and Alan

Lowe et al1. These changes were compared with the normoocclusion control

group.

The mean differences in the dimensions of nasopharynx, velopharynx,

glossopharynx and hypopharynx of Class I group and Class II Group following

orthodontic treatment were compared (Table 7 and Table 10).

In our study, there was a significant overall reduction in the pharyngeal

airway after orthodontic treatment in Class I group. Compared to the

palatopharynx and oropharynx, the cross sectional areas of glossopharynx and

hypopharynx were significantly reduced (p value 0.001) more after the

treatment. Nasopharynx and oropharynx were reduced by 0.26mm and 0.6mm

respectively whereas glossopharynx and hypopharynx were reduced by

0.73mm and 1.14mm respectively. These findings were coinciding with the

Discussion

60

results of the study by Qingzhu Wang 70,

, Derya Germec-Cakan et al22,

and Yu

Chen85

. This amount of decrease cannot be explained by growth changes and

might be due to narrowing of the tongue space after incisor retraction.

But our results differed from the result of a study by Valiathan et al 52

in

which they demonstrated that oropharyngeal volumes did not show significant

change after orthodontic treatment with extraction of four premolars in

adolescents. This negative finding may be attributed to mandibular growth as

their study group had subjects in the age range of 11 – 13 years and the high

variability of oropharyngeal volume.

However, in our study, it was not the same in case of Class II group. The

nasopharyngeal airway dimensions were reduced after treatment significantly

(p value 0.002) but the velopharynx, glossopharynx and hypopharynx areas

were significantly increased by 1.05mm , 1.29mm and 2.31mm respectively (p

value 0.001) following treatment. A possible explanation for this increase in

airway might be an increase in posterior tongue space after forward movement

of mandible due to the use of orthodontic mechanotherapy for Class II

corrections. The average mesial molar movement was 3.23 mm (TABLE 12) in

this group.

The importance of hyoid bone lies in its distinctive relationships. It has

no bony articulations but provides attachment for muscles, ligaments,

mandible, fascia of the pharynx and cranium 29, 73

. A close association of the

hyoid bone to the cartilages of the larynx also suggests the importance of hyoid

in the performance of both respiration and deglutition. The anteroposterior

Discussion

61

position of the hyoid bone follows the anteroposterior position of the chin.

When the mandible was rotated in counter clockwise direction, the suprahyoid

muscles pulled the hyoid bone to move into a more anterior position, and when

the mandible was rotated in a clockwise direction, the hyoid bone moved

posteriorly.

Yu Chen et al75

and Qingzhu Wang et al85

demonstrated a significant

change in position of hyoid bone following orthodontic treatment in Class I

bimaxillary protrusion cases. The hyoid bone was retracted postero inferiorly

after treatment. Masayoshi Kawakami et al55

confirmed that the vertical and

horizontal spaces around the tongue were maintained postoperatively with the

backward and downward movement of the hyoid, which compensates for the

reduction in oral volume after mandibular setback surgeries. The hyoid position

depends on the relative balance of muscle attachment from the base of the

cranium bilaterally and the region of the mandibular symphysis14

.

The mean differences in the hyoid bone positions of Class I group and

Class II Group following orthodontic treatment were shown in table 8 and table

11.

In our study, there was a significant change in the hyoid position in

relation to the point RGN (Retrognathion), Third cervical vertebra (C3) and

Sella point in both Class I and Class II groups. The hyoid bone was found to be

retracted postero inferiorly in Class I group. The amount of retraction was 1.04

mm and 1.30 mm in horizontal and vertical direction (Table 8). Findings of our

Discussion

62

study were coinciding with that of the study by Qingzhu Wang 70

. The inferior

movement of the hyoid bone seen in the present study was consistent with the

findings of other studies, showing that this movement is an adaptation

preventing an encroachment of the tongue into the pharyngeal airway 85

. Our

findings confirmed that the horizontal spaces around the tongue (TB-TPPW)

were decreased with the downward movement of the hyoid bone caused by the

retraction of incisors. But in class II group of our study the hyoid bone was

found to be shifted antero superiorly.

Comparison of the airway dimensions and hyoid positions of Class I and

Class II to the normoocclusion subjects reveals the following:

Pretreatment nasopharynx and velopharynx areas of class I and class II

subjects were wider than the normoocclusion subjects. But the hypopharynx

area was constricted in both Class I and Class II groups with highly significant

reduction in Class II groups which is attributable to the retrognathic mandible

and posteriorly positioned tongue. Vertical length of the airway was also

reduced in Class II group in comparison with that of Class I group and

normoocclusion group.

After treatment the overall pharyngeal space was significantly reduced

in Class I group, with only velopharynx and glossopharynx areas

approximating to the values of the normoocclusion group. Whereas in Class II

group, there was a significant widening of the velopharynx, glossopharynx and

hypopharynx areas attributable to the forward positioning of the mandible after

Discussion

63

the treatment which may be due to the orthodontic mechanotherapy to correct

class II condition which includes the use of inter arch elastics or protraction of

molars or fixed functional appliance during treatment. Whereas the

hypopharynx area was not widened to the normal levels.

At baseline the Hyoid bone was positioned antero superiorly in Class I

subjects and postero superiorly in class II subjects when compared to the

normoocclusion groups. After treatment the hyoid was retracted postero

inferiorly in Class I group attributable to the constriction in lower airway.

Whereas in class II group the hyoid bone was shifted anterosuperiorly after

treatment which can be attributed to the forward movement of mandible due to

the orthodontic mechanotherapy to correct class II condition which includes the

use of inter arch elastics or protraction of molars or fixed functional appliance

during treatment. The changes were statistically significant in both the

conditions with p values less than 0.05.

There was no statistically significant (p value > 0.05) sexual

dimorphism in the changes of pharyngeal airway dimensions and hyoid

positions of the study groups.

Summary and Conclusion

64


Pharyngeal airway dimension plays an important role in dentofacial

development. The malocclusion type and sagittal jaw relationship had been

proved to affect the pharyngeal airway dimensions in healthy subjects with

average growth pattern. This study had been undertaken to correlate subjects

with normal respiratory function with Class I and Class II malocclusions.

There was a significant difference in the changes in the airway dimensions

and hyoid bone position between Class I and Class II groups following

non-surgical orthodontic treatment.

Pretreatment nasopharynx, glossopharynx and velopharynx areas of Class I

and Class II malocclusion subjects were marginally wider than the

normoocclusion subjects. But the hypopharynx area was significantly

constricted in both Class I and Class II groups with highly significant

reduction (p value < 0.001) in Class II groups.

In Class I malocclusion group there was a significant decrease in overall

upper airway dimensions, with more reduction in glossopharynx and

hypopharynx areas following non-surgical orthodontic treatment with only

velopharynx and glossopharynx areas approximating to the values of the

normoocclusion group.

Unlike in Class I malocclusion group, Class II malocclusion group

revealed diverse changes in airway dimensions after orthodontic treatment.

Nasopharynx was constricted minimally and the glossopharynx and


65

hypopharynx areas were widened significantly. Whereas the hypopharynx

area was not widened to the level of normoocclusion group.

Pretreatment Hyoid bone position was antero superior in Class I subjects

and postero superior in Class II subjects when compared to the

normoocclusion groups. After treatment the hyoid was retracted postero

inferiorly in Class I group. Whereas in Class II group the hyoid bone was

shifted anterosuperiorly after treatment. Still the hyoid position was not

approximated to that of normoocclusion group.

There was no statistically significant (p value > 0.05) sexual dimorphism

in both pharyngeal airway dimensions and hyoid bone positions in all three

groups.

Future prospects:

Further studies may be aimed at long-term effects of nonsurgical

orthodontic treatment on pharyngeal airway and hyoid positions.

It was evident that non-surgical orthodontic therapy has an effect on

pharyngeal airway dimensions. Future studies may be carried out to

evaluate the changes in airway dimensions following surgical

orthodontic therapy.

Future studies may be done to evaluate the airway flow capacity in

different malocclusions using 3D imaging systems.

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